Multipurpose connection/reception device for nuclear magnetic resonance imager

ABSTRACT

The universal connector/receiver device for a nuclear magnetic resonance imager ( 1 ) of the invention is provided with at least one radiofrequency transmitter coil ( 5 ) and with at least one standard radiofrequency receiver coil ( 6 ). According to the invention, the device comprises at least one independent radiofrequency receiver coil ( 14 ) adapted to the shape and/or size of an item to be investigated, for the purpose of transforming an electromagnetic signal induced by nuclear magnetic resonance into an electrical signal, said independent radiofrequency receiver coil ( 14 ) being connected to a receiver coupling loop ( 20 ) serving to provide magnetic coupling with the standard radiofrequency receiver coil ( 6 ).

The present invention relates to the technical field of nuclear magneticresonance (NMR) imaging, and also to applications of this technique inthe medical field.

More particularly, the invention relates to a universalconnector/receiver device making it possible to adapt various types ofradiofrequency (RF) receiver coil to a given imager.

In general, nuclear magnetic resonance imagers are associated with amagnetic system that generates a magnetic field that varies in threedimensions, in a space occupied by the item under investigation, so asto obtain a different resonant frequency at each point thereof. Aradiofrequency transmission coil is immersed in the magnetic field inorder to transmit an electromagnetic wave which, as a function of thefrequency of said wave and of the magnetic field at each point of theitem under investigation, induces resonance that is accompanied by thetransmission of a magnetic signal. A radiofrequency receiver coil servesto detect this signal induced by resonance and to transform it into anelectrical signal. The radiofrequency transmitter or receiver coils towhich the invention relates comprise means for transforming electricalsignals into an electromagnetic wave for a transmitter coil or, viceversa for a receiver coil. These means are also known as antennas.

The radiofrequency transmitter coil and the radiofrequency receiver coilare generally connected respectively to a radiofrequency transmissioncontrol system and to a device for building a two- or three-dimensionalimage of the item under investigation, these means together constitutinga nuclear magnetic resonance imager.

In general, the radiofrequency receiver coil is adapted to the shapeand/or size of the item under investigation. This item can be any itemthat is observable using a nuclear magnetic resonance imager. Ingeneral, it corresponds to a portion of the body of a patient.

Thus, the radiofrequency receiver coil is often selected from amongst aset of “standard” radiofrequency receiver coils of characteristics andperformance that vary as a function of the shape and/or size of the itemunder investigation.

Each model of imager is often provided with a proprietary connector thatcan be fitted to connectors coming from the same set of standardradiofrequency receiver coils.

A user possessing one particular model of imager generally cannot fitradiofrequency receiver coils that do not correspond to that model or tothe design date of the imager in question. In addition, a set ofstandard radiofrequency receiver coils corresponding to one particularmodel of imager generally does not make it possible to cover the entireextent of medical applications of interest to all of the users in agiven hospital establishment.

The problem faced by the user is thus associated with lack ofcompatibility or with the magnitude of the investment required toacquire all of the imagers needed for the intended applications.

It is specifically the object of the invention to propose a deviceenabling this lack of compatibility to be mitigated.

To satisfy the needs of users of imaging techniques, the inventionprovides a universal connector/receiver device for a nuclear magneticresonance imager provided with at least one radiofrequency transmittercoil and with at least one standard radiofrequency receiver coil,

-   -   the device being characterized in that it comprises at least one        independent radiofrequency receiver coil adapted to the shape        and/or size of an item to be investigated, for the purpose of        transforming an electromagnetic signal induced by nuclear        magnetic resonance into an electrical signal, said independent        radiofrequency receiver coil being connected to a receiver        coupling loop serving to provide magnetic coupling with the        standard radiofrequency receiver coil.

Although the universal connector/receiver device described above enablesthe field of user applications to be extended, the frequency of theelectromagnetic waves used generally constitutes a characteristic thatis invariable and predetermined for any particular type of imager used.Thus, the development of nuclear magnetic resonance imagers is tendingtowards applying stronger magnetic fields, which leads to the need tochange the frequency of the electromagnetic waves used. Furthermore,independently of the magnetic field used, the user can be led toenvisage working at different frequencies as a function of the type ofnucleus that is to be made to resonate. As a result, imagers that aregenerally suitable for working at a single frequency only, once moreconstitute a limitation on the fields of application that can beenvisaged.

It is specifically an object of a particular embodiment of the inventionto use a universal connector/receiver device that makes it possible totransmit an electromagnetic wave at a frequency that can be adapted tothe intended application.

This particular embodiment thus provides a universal connector/receiverdevice as described above, characterized in that it includes at leastone independent radiofrequency transmitter coil connected to at leastone transmitter coupling loop providing magnetic coupling with theradiofrequency transmitter coil, and in that a frequency synthesizer isinterposed between the output of the transmitter coupling loop and aninput of the receiver coupling loop in order to transmit anelectromagnetic wave having a specific frequency, and to adapt thefrequency of the electrical signal coming from the independentradiofrequency receiver coil to a frequency of the imager.

Various other characteristics appear from the following descriptiongiven with reference to the accompanying drawings which show embodimentsof the invention as non-limiting examples.

FIG. 1 shows an embodiment of the invention enabling different types ofindependent radiofrequency receiver coil to be fitted to a given imager.

FIG. 2 shows another embodiment of the invention further making itpossible to transmit an electromagnetic wave having a specific frequencyand to adapt the frequency of the electrical signal delivered by theindependent radiofrequency receiver coil to a frequency of the imager.

The embodiment shown in FIG. 1 shows all of the components of an imagergiven overall reference 1. One of the functions of the imager 1 is totransmit an electromagnetic wave of given amplitude and frequency. Thisfunction is provided by a transmitter system that generally forms anintegral portion of the imager 1. At its upstream end the transmittersystem comprises a control system 2 for generating an electrical signalwhich is subsequently amplified by an amplifier 3 connected to saidcontrol system 2. Tuning and matching means 4 are disposed downstreamfrom the amplifier in order to filter the amplified signal and optimizethe efficiency of amplification. The end of the transmitter system isconnected to a radiofrequency transmitter coil 5 for transforming theamplified, matched, and tuned electrical signal into an electromagneticwave. The radiofrequency transmitter coil 5 is generally inserted in themagnetic field generated by a magnet (not shown). In most cases, thetransmitter coil 5 is disposed in such a manner as to surround the itemunder investigation within said magnetic field. The characteristics ofthe electromagnetic wave transmitted by the radiofrequency transmittercoil 5 are generally a frequency substantially equal to 64 megahertz(MHz) with a passband of approximately 200 kilohertz (kHz) for amagnetic field of 1.5 teslas (T). Nevertheless, these characteristicsmay vary as a function of the magnetic field used, and also as afunction of the type of analysis performed.

The imager 1 may include means enabling different types ofradiofrequency coil to be fitted thereto. In addition, it may includeother means enabling adjustment parameters of the tuning and matchingmeans 4 and also of the amplifier 3 to be varied.

As shown in FIG. 1, the imager 1 includes at least one standardradiofrequency receiver coil 6. The standard radiofrequency receivercoil 6 may itself comprise a coil proper 7, tuning and matching means 8and decoupling means 9. It may also include a preamplifier 10.

In general, the standard radiofrequency receiver coil 6 forms part of aset of standard radiofrequency receiver coils each of which is providedwith a standard connector 11 a suitable for fitting to the connector 11b of the model of imager in use. The connection system 11 of thestandard radiofrequency receiver coils associated with a particularmodel of imager can vary as a function of the model and of the designdate of said coil and/or of the imager in use.

The imager 1 also includes a radiofrequency receiver 12 provided withthe connector 11 b enabling the electrical signal coming from thestandard radiofrequency receiver coil to be received.

Naturally, the imager 1 includes digital processor means (not shown) forbuilding two- or three-dimensional images of the item underinvestigation.

In accordance with the invention, the nuclear magnetic resonance imageris associated with a universal connector/receiver device 13 comprisingat least one independent radiofrequency receiver coil 14. This coil isindependent in that it does not constitute a component of the imager 1as described above. The independent radiofrequency receiver coil 14 isfitted with a coil proper 15 for transforming said signal induced byresonance into an electrical signal. This coil 14, and in particular thecoil proper 15, is adapted to the shape and/or size of the item underinvestigation. The independent radiofrequency receiver coil can bepositioned so as to surround the item under investigation. It may alsobe placed close to the item under investigation. Generally, like theitem under investigation, it is disposed within the magnetic fieldgenerated by the magnet associated with the imager. In addition, it mayadvantageously be disposed inside the radiofrequency transmitter coil 5.

The independent radiofrequency receiver coil 14 preferably comprisestuning and matching means 16 to which the coil proper 15 is attached. Inparticular, said independent radiofrequency receiver coil 14 may includedecoupling means 17. These decoupling means 17, also referred to asisolating devices, serve to minimize coupling between the radiofrequencytransmitter coil 5 and the independent radiofrequency receiver coil 14.Such coupling has two harmful consequences:

-   -   the first is to reinforce the field induced by the transmitted        electromagnetic wave, the independent radiofrequency receiver        coil 14 then acting as a magnetic flux concentrator which        disturbs the normal operation of the imager; and    -   the second is caused by unacceptable heating of the item under        investigation which, in the medical field, generally corresponds        to a portion of the body of a patient, where heating can        endanger the patient if a certain limit is exceeded.

In an advantageous embodiment, an electronic control circuit 18 isconnected to the tuning and matching means 16 and/or to the decouplingmeans 17. The electronic control circuit 18 serves in particular toadjust the tuning and matching means 16 and the decoupling means 17.

The device preferably comprises a monitor loop 19 providing magneticcoupling with the radiofrequency transmitter coil 5 and connected to theelectronic control circuit 18. The monitor loop 19 serves in particularto servo-control the decoupling means 17 of the independentradiofrequency receiver coil 14 relative to the electromagnetic wavetransmitted by the radiofrequency transmitter coil 5, and to do so bymeans of the electronic circuit 18.

The magnetic coupling of the monitor loop 19 with the radiofrequencytransmitter coil 5 can be implemented in any way. This coupling makes itpossible to transfer, in the form of an electrical signal, theelectromagnetic wave transmitted by the radiofrequency transmitter coil5 to the electronic control circuit 18.

In a particular embodiment, the independent radiofrequency receiver coil14 is selected from standard radiofrequency receiver coils that areavailable on the market.

In accordance with the invention, the independent radiofrequencyreceiver coil 14 is connected to a receiver coupling loop 20 providingmagnetic coupling with the standard radiofrequency receiver coil 6.

It follows that for a given imager, it is possible to use any type ofindependent radiofrequency receiver coil 14, regardless of the model andthe design date of the imager.

The receiver coupling loop 20 can be positioned close to or preferablyinside the standard radiofrequency receiver coil 7 proper.

Generally, the receiver coupling loop 20 and the standard radiofrequencyreceiver coil 6 are both located outside the magnetic field generated bythe magnet associated with the imager. Under such circumstances, thefunction of the receiver coupling loop 20 is to transfer an electricalsignal coming from the independent radiofrequency receiver coil 14.

In another method of use, the receiver coupling loop 20 and the standardradiofrequency receiver coil 6 are located within the magnetic fieldgenerated by the magnet associated with the imager. The receivercoupling loop 20 and the coil 7 then serve not only to transfer anelectrical signal coming from the independent radiofrequency receivercoil 14, but also to receive the electromagnetic signal induced bynuclear magnetic resonance in the item under investigation.

A coupling preamplifier 21 is preferably inserted between theindependent radiofrequency receiver coil 14 and the receiver couplingloop 20.

It is possible to envisage a device having a plurality of independentradiofrequency receiver coils 14 connected by magnetic coupling via asmany receiver coupling loops 20 with as many standard radiofrequencyreceiver coils 16 themselves connected to the imager.

In a particular embodiment of the invention, two independentradiofrequency receiver coils 14 disposed in quadrature are connected totwo receiver coupling loops 20 providing magnetic coupling with twostandard radiofrequency receiver coils 6 of the imager 1. By placing theindependent radiofrequency receiver coils 14 in quadrature, each of themis disposed in such a manner that the main axes of the fields form anangle of approximately 90°. In this particular configuration, it isgenerally necessary to provide a device that enables the electricalsignals coming from the standard radiofrequency receiver coils 6 to beadded together.

In a variant of the preceding embodiment, two independent radiofrequencyreceiver coils 14 placed in quadrature are connected to the inputs of anadder device (not shown) having at least two inputs and one output, saidoutput being connected to the receiver coupling loop 20. This embodimentenables a single receiver coupling loop 20 and a single standardradiofrequency receiver coil 6 to be used. It should be observed that itis possible to envisage using a number of independent radiofrequencyreceiver coils 14 that is greater than two.

In a particular embodiment of the invention, the universalconnector/receiver device enables an electromagnetic wave to betransmitted at a specific frequency different from the frequency of theimager, and to adapt the frequency of the electrical signal coming fromthe independent radiofrequency receiver coil 14 to the frequency of theimager. This also makes it possible to cause nuclei other than those ofhydrogen atoms to enter into resonance, where the resonant frequency ofhydrogen is approximately 42 MHz, for a magnetic field of 1 T. As aresult, it is possible to envisage causing the nuclei of molecules suchas phosphorus or helium to enter into resonance. In addition, progressin the field of nuclear magnetic resonance imaging is tending towardsusing ever stronger magnetic fields, e.g. 3 T fields, such that thefrequencies of the transmitted electromagnetic waves need to be adaptedaccordingly.

As shown in FIG. 2, in this particular embodiment of the invention, theuniversal connector/receiver device 13 includes at least one independentradiofrequency transmitter coil 30 connected to at least one transmittercoupling loop 31 providing magnetic coupling with the radiofrequencytransmitter coil 5. The universal receiver device 13 further comprises afrequency synthesizer 32 interposed between the output from thetransmitter coupling loop 31 and the input of the receiver coupling loop20. The frequency synthesizer 32 enables an electromagnetic wave havinga specific frequency to be transmitted and enables the frequency of theelectrical signal coming from the independent radiofrequency receivercoil 14 to be adapted to a frequency of the imager 1. The frequencysynthesizer 32 is interposed at the output of the transmitter couplingloop 31 by means of a frequency adapter device 33 enabling the frequencyof the electrical signal which depends on the imager 1 into a specificfrequency. Similarly, the synthesizer 32 is interposed at the input ofthe receiver coupling loop 20 by means of another frequency adapterdevice 34 (e.g. a mixer) enabling the frequency of the electrical signalcoming from the independent radiofrequency receiver coil 14 to beadapted to the frequency of the imager 1.

In a preferred embodiment, the frequency adapter device 33 is connectedto an independent radiofrequency transmitter coil 30 via an amplifier35.

In another preferred embodiment, the independent radiofrequencytransmitter coil 30 includes tuning and matching means.

The invention makes it possible, advantageously, to use electromagneticwaves of frequency that can be adapted to a specific frequency which isdifferent from the frequency of the imager. This makes it possible tocause nuclei of atoms other than hydrogen, e.g. atoms of phosphorus orhelium to be caused to enter into resonance. This also makes it possibleto adapt the frequency of the electromagnetic waves to magnetic fieldsthat are stronger than those commonly in use.

The invention is not limited to the examples described and shown sincevarious modifications can be applied thereto without going beyond theambit of the invention.

1. A universal connector/receiver device for a nuclear magneticresonance imager (1) provided with at least one radiofrequencytransmitter coil (5) and with at least one standard radiofrequencyreceiver coil (6), the device being characterized in that it comprisesat least one independent radiofrequency receiver coil (14) adapted tothe shape and/or size of an item to be investigated, for the purpose oftransforming an electromagnetic signal induced by nuclear magneticresonance into an electrical signal, said independent radiofrequencyreceiver coil (14) being connected to a receiver coupling loop (20)serving to provide magnetic coupling with the standard radiofrequencyreceiver coil (6).
 2. A device according to claim 1, characterized inthat a coupling preamplifier (21) is inserted between the independentradiofrequency receiver coil (14) and the receiver coupling loop (20).3. A device according to claim 1, characterized in that the independentradiofrequency receiver coil (14) includes tuning and matching means(16).
 4. A device according to claim 1, characterized in that theindependent radiofrequency receiver coil (14) includes decoupling means(17).
 5. A device according to claim 1, characterized in that theindependent radiofrequency receiver coil (14) is selected from standardradiofrequency receiver coils.
 6. A device according to claim 1,characterized in that the receiver coupling loop (20) is positionedinside the standard radiofrequency receiver coil (6).
 7. A deviceaccording to claim 1, characterized in that the receiver coupling loop(20) and the standard radiofrequency receiver coil (6) are locatedwithin a magnetic field generated by a magnet associated with theimager.
 8. A device according to claim 2, characterized in that anelectronic control circuit (18) is connected to the tuning and matchingmeans (16) and/or to the decoupling means (17).
 9. A device according toclaim 1, characterized in that two independent radiofrequency receivercoils (14) disposed in quadrature are connected to two receiver couplingloops (20) providing magnetic coupling with two standard radiofrequencyreceiver coils (6) of the under imager (1).
 10. A device according toclaim 1, characterized in that two independent radiofrequency receivercoils (14) disposed in quadrature are connected to the inputs of anadder device having at least two inputs and one output, said outputbeing connected to the receiver coupling loop (20).
 11. A deviceaccording to claim 8, characterized in that it includes a monitor loop(19) providing magnetic coupling with the radiofrequency transmittercoil (2) and connected to the electronic control circuit (18).
 12. Adevice according to claim 1, characterized in that it includes at leastone independent radiofrequency transmitter coil (30) connected to atleast one transmitter coupling loop (31) providing magnetic couplingwith the radiofrequency transmitter coil (5), and in that a frequencysynthesizer (32) is interposed between the output of the transmittercoupling loop (31) and an input of the receiver coupling loop (20) inorder to transmit an electromagnetic wave having a specific frequency,and to adapt the frequency of the electrical signal coming from theindependent radiofrequency receiver coil (14) to a frequency of theimager (1).
 13. A device according to claim 12, characterized in thatthe independent radiofrequency transmitter coil (30) is fed via anamplifier (35) which is interposed between the transmitter coupling loop(31) and said independent radiofrequency transmitter coil (30).
 14. Adevice according to claim 12, characterized in that the independentradiofrequency transmitter coil (30) includes tuning and matching means.